The ventilatory effects of auto-positive end-expiratory pressure development during cardiopulmonary resuscitation.

OBJECTIVE: Auto-positive end-expiratory pressure (auto-PEEP) is a physiologic phenomenon defined as the positive alveolar pressure that exists at the end of expiration. Normally, the alveolar pressure is near zero at the end of expiration. However, certain ventilatory and/or physiologic paradigms can cause the development of auto-PEEP during cardiopulmonary resuscitation (CPR). Auto-PEEP has a detrimental cardiovascular effect similar to that of positive end-expiratory pressure that is intentionally applied to the ventilatory circuit in a mechanically ventilated patient. The connection between auto-PEEP and its cardiovascular effects, however, may go undetected. In this study, the effect that ventilatory factors have on auto-PEEP in a simulation of patients with lung disease undergoing CPR was delineated. DESIGN: A case control study. SETTING: Laboratory of a university hospital anesthesia department. SUBJECTS: A baseline quantification of breathing patterns that occur during CPR was obtained by recording observed respiratory rate and relative tidal volume during treatment of in-hospital cardiac arrests. MEASUREMENTS AND MAIN RESULTS: A test lung was set up to mimic a series of different airway resistances and lung compliances as would be seen in different types of pulmonary pathology. A sensitivity analysis was performed on each of the factors of respiratory rate, tidal volume, and inspiratory/expiratory ratio as to the effect each of these factors has on the development of auto-PEEP. Our study suggests that in various combinations of airway resistances and lung compliances, auto-PEEP can be generated to substantial levels depending on the methods of ventilation performed. CONCLUSION: We conclude from our findings that ventilation techniques during CPR may need to be altered to avoid the development of what may be a hemodynamically significant level of auto-PEEP.

On the dynamic performance of the Abbott Safeset blood-conserving arterial line system.

OBJECTIVE: Critically ill patients frequently have indwelling arterial lines placed during their Intensive Care Unit stay. The lines are used to monitor blood pressure continuously, administer drugs and to draw blood for a variety of physiologic tests. Several blood-conserving arterial line systems have been developed to eliminate the need to discard blood in the process of obtaining undiluted and uncontaminated blood samples. The purpose of this study was to evaluate the dynamic performance of one such system the Abbott Clinical Care System Safeset blood conserving arterial line system - in comparison to a conventional arterial line system. METHODS: We studied ninety-nine patients who had indwelling arterial lines placed during surgery and who were admitted to our Surgical Intensive Care Unit (SICU). The patients were randomly placed into one of two groups. The control group received a conventional indwelling arterial line system; the experimental group received the Abbott Safeset system. We measured the damping coefficient and resonant frequency daily in order to evaluate and compare the dynamic performance of the two systems. We also measured discard volumes (in the control group) and blood sample sizes during the patients' stays in the SICU. RESULTS: The two patient groups were similar in regards to demographics and baseline clinical characteristics. A median 3 ml of blood per draw and 17.5 ml of blood per patient was discarded in purging the conventional arterial line system while, by design, no blood was discarded with the experimental system. There was no difference between the two groups with regard to damping coefficient. Both systems were underdamped. However, the conventional arterial line system had a significantly higher resonant frequency (16.7 Hz) compared to the Safeset system (12.5 Hz). CONCLUSIONS: Because the Abbott Safeset blood-conserving arterial line system is underdamped and has a lower resonant frequency compared to the traditional arterial system, it may overestimate systolic blood pressure, particularly in patients with high heart rates.